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Towards Constraints on the Epoch of Reionization: a Phenomenological Approach

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Towards Constraints on the Epoch of Reionization: a Phenomenological Approach University of Pennsylvania ScholarlyCommons Publicly Accessible Penn Dissertations 2015 Towards Constraints on the Epoch of Reionization: A Phenomenological Approach Matthew Malloy University of Pennsylvania, [email protected] Follow this and additional works at: https://repository.upenn.edu/edissertations Part of the Astrophysics and Astronomy Commons, and the Physics Commons Recommended Citation Malloy, Matthew, "Towards Constraints on the Epoch of Reionization: A Phenomenological Approach" (2015). Publicly Accessible Penn Dissertations. 1875. https://repository.upenn.edu/edissertations/1875 This paper is posted at ScholarlyCommons. https://repository.upenn.edu/edissertations/1875 For more information, please contact [email protected]. Towards Constraints on the Epoch of Reionization: A Phenomenological Approach Abstract Based on observations of the early Universe, we know that shortly after the Big Bang, the Universe was composed almost entirely of neutral hydrogen and neutral helium. However, observations of nearby quasars suggest that the gas between galaxies today is neutral to less than one part in 10^4. Thus, it must be the case that some process occurred that stripped the electrons from almost all atoms in the intergalactic medium. Understanding the timing and nature of this process, dubbed ``reionization'', is one of the great outstanding problems in astrophysics and cosmology today. In this thesis, we develop several methods for utilizing existing and future measurements in order to make progress toward this end. We begin by proposing two novel approaches for searching for signatures of underlying neutral hydrogen in the Lya and Lyb forest of distant quasars. We show that, if the Universe is >5% neutral at z ~ 5.5, then damping-wing absorption from neutral hydrogen and absorption from primordial deuterium should leave observable imprints in the Lya and Lyb forest, respectively. Furthermore, the presence of neutral islands should qualitatively alter the size distribution of absorbed regions. We continue by discussing the ability for the intergalactic medium to retain a thermal memory of the reionization process at redshifts z ~ 5, which in turn affects the small-scale structure in the Lya forest. Motivated by this, we model the temperature of the intergalactic medium after reionization and develop a temperature measurement technique that should be able to distinguish between scenarios where reionization ends at z ~ 6 and at z ~ 10. Lastly, we turn our attention to 21-cm observations during reionization. We demonstrate that, while precise mapping of 21-cm emission from neutral hydrogen should be infeasible by first and second generation interferometers, it may be possible to make crude maps of the reionization process and identify individual ionized regions. This would provide us with direct confirmation that we are observing reionization and provide information regarding its timing and the nature of the ionizing sources. Degree Type Dissertation Degree Name Doctor of Philosophy (PhD) Graduate Group Physics & Astronomy First Advisor Adam Lidz Keywords 21-cm, Cosmology, Large Scale Structure, Lyman Alpha Forest, Reionization, Theory Subject Categories Astrophysics and Astronomy | Physics This dissertation is available at ScholarlyCommons: https://repository.upenn.edu/edissertations/1875 TOWARDS CONSTRAINTS ON THE EPOCH OF REIONIZATION: A PHENOMENOLOGICAL APPROACH Matthew Malloy A DISSERTATION in Physics and Astronomy Presented to the Faculties of the University of Pennsylvania in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy 2015 Supervisor of Dissertation Graduate Group Chairperson Adam Lidz Marija Drndi`c Professor, Physics and Astronomy Professor, Physics and Astronomy Dissertation Comittee: James Aguirre, Assistant Professor, Physics and Astronomy Cullen Blake, Assistant Professor, Physics and Astronomy Elliot Lipeles, Professor, Physics and Astronomy Masao Sako, Professor, Physics and Astronomy TOWARDS CONSTRAINTS ON THE EPOCH OF REIONIZATION: A PHENOMENOLOGICAL APPROACH COPYRIGHT c 2015 Matthew Malloy This work is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/4.0/ To JM iii Acknowledgements This thesis truly would not have been possible without a great number of people. First and foremost, I would like to thank my advisor, Adam Lidz, whose endless ability to find interesting and important problems made this an exciting and rewarding experience and whose approach toward tackling those problems has invaluably and irreversibly affected my own. I could not have asked for a better advisor. I would also like to thank collaborators Judd Bowman and Piyanat “Boom” Kittiwisit at ASU, who gave me a greater appreciation for things on the experimental side, and also Andrei Mesinger, Ian McGreer, and Valentina D’Odorico. During my time at Penn, I benefited immensely from conversations and time spent with Garrett Goon and Rami Vanguri. Additionally, I would like to thank the Machine Learning Club and Alan Meert, who taught me literally half of what I have learned in the last year. Ross Anderson, Devin Kennedy, and Miles Wheeler – your inexplicable eagerness to contribute with algorithmic consults was both helpful and touching. I would also like to thank Jessie Taylor for valuable and interesting discussions. I am very fortunate to have been in Philadelphia at the same time as Caitlin Beecham, Chris Bryan, Tom Caldwell, Susan Fowler, Donnie Galvano, Bennet Huber, Andrew Mc- Carthy, Tom Pacific, Doug Schaefer, Katie Schmaling Meert, Elizabeth Stokes, Biquan Su, Debra Van Camp, and Haotian Xian, who, among many other things, played an essential role in me maintaining my sanity. I would also like to thank my parents and my sister who have been a constant source of love and support from the very beginning. Last, but not least, I would like to thank Dingding Jia for her unwavering support and encouragement. iv ABSTRACT TOWARDS CONSTRAINTS ON THE EPOCH OF REIONIZATION: A PHENOMENOLOGICAL APPROACH Matthew Malloy Adam Lidz Based on observations of the early Universe, we know that shortly after the Big Bang, the Universe was composed almost entirely of neutral hydrogen and neutral helium. However, observations of nearby quasars suggest that the gas between galaxies today is neutral to less than one part in 104. Thus, it must be the case that some process occurred that stripped the electrons from almost all atoms in the intergalactic medium. Understanding the timing and nature of this process, dubbed “reionization”, is one of the great outstanding problems in astrophysics and cosmology today. In this thesis, we develop several methods for utilizing existing and future measurements in order to make progress toward this end. We begin by proposing two novel approaches for searching for signatures of underlying neutral hydrogen in the Ly α and Ly β forest of distant quasars. We show that, if the Universe is & 5% neutral at z 5.5, then damping-wing absorption from neutral hydrogen ∼ and absorption from primordial deuterium should leave observable imprints in the Ly α and Ly β forest, respectively. Furthermore, the presence of neutral islands should qualitatively alter the size distribution of absorbed regions. We continue by discussing the ability for the intergalactic medium to retain a thermal memory of the reionization process at redshifts z 5, which in turn affects the small- ∼ scale structure in the Ly α forest. Motivated by this, we model the temperature of the intergalactic medium after reionization and develop a temperature measurement technique that should be able to distinguish between scenarios where reionization ends at z 6 and ∼ at z 10. ∼ v Lastly, we turn our attention to 21-cm observations during reionization. We demonstrate that, while precise mapping of 21-cm emission from neutral hydrogen should be infeasible by first and second generation interferometers, it may be possible to make crude maps of the reionization process and identify individual ionized regions. This would provide us with direct confirmation that we are observing reionization and provide information regarding its timing and the nature of the ionizing sources. vi Contents Title i Copyright ii Dedication iii Acknowledgements iv Abstract v Contents vii List of Tables xi List of Figures xii 1 First Things First 1 1.1 CosmicContext.................................. 1 1.2 TheShouldersofGiants . .. .. .. .. .. .. .. .. 7 1.2.1 The Ly α Forest ............................. 7 1.2.1.1 Evolution of τeff ........................ 14 1.2.1.2 Dark Pixel Covering Fraction . 20 1.2.1.3 Damping Wing Redward of Ly α ............... 24 vii CONTENTS 1.2.1.4 IGMTemperature . .. .. .. .. .. .. 30 1.2.2 The21-cmLine.............................. 37 1.2.2.1 The Intensity of the 21-cm Line . 38 1.2.2.2 21-cm Fluctuations with Interferometers . 44 1.2.2.3 Brief Description of 21-cm Interferometric Experiments . 54 1.2.2.4 The Global 21-cm Signal . 60 1.2.3 The Cosmic Microwave Background . 65 1.2.3.1 Thomson Scattering Optical Depth, τe ............ 66 1.2.3.2 Kinetic Sunyaev-Zel’dovich Effect . 70 1.2.4 Ly α Emitters............................... 72 1.2.4.1 Clustering of Ly α Emitters.................. 72 1.2.4.2 Ly α EmitterFraction .. .. .. .. .. .. 75 1.2.5 Luminosity Function Measurements . 76 1.3 MovingForward ................................. 80 2 How to Search for Islands of Neutral Hydrogen in the z 5.5 IGM 82
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